A variety of power supply systems for supplying power from a secondary battery to a load are used in hybrid cars and others. In such a power supply system, it is necessary to properly detect abnormalities in a secondary battery.
In this respect, for example, Japanese Patent Laying-Open No. 2002-084669 (referred to as Patent Document 1 hereinafter) discloses a battery pack configured such that a plurality of cell groups each configured to include a plurality of electric cells connected in series are connected in series. For this battery pack, cell-state monitoring means for monitoring a state of each electric cell is provided to allow sensing of abnormalities for each electric cell. In particular, in the configuration disclosed in Patent Document 1, power supply to the cell-state monitoring means is at least partially stopped during a period of time in which the output from the cell-state monitoring means is not referred to by the higher-level abnormality monitoring means, so that power consumption by the cell-state monitoring means can be reduced.
Furthermore, Japanese Patent Laying-Open No. 11-234801 (referred to as “Patent Document 2” hereinafter) discloses a battery ECU detecting a battery abnormal condition based on voltage data or temperature data. In this battery ECU, when any abnormality occurs in a sensor itself that detects the abnormality of the battery, a ventilating fan or an in/out switching valve is switched appropriately so that gases produced from the battery can quickly be exhausted from the car even when the battery abnormal condition takes place repeatedly.
However, the configuration disclosed in Patent Document 1 is unable to sense the abnormality of the cell-state monitoring means itself that monitors the abnormality of the secondary battery. Therefore, during the abnormal condition of the cell-state monitoring means, the secondary battery may not be controlled properly due to wrong information.
On the other hand, in the configuration disclosed in Patent Document 2, as for a sensor determining voltage data or temperature data, a failure in the sensor itself is sensed at the time of hardware failures such as a disconnection or a short-circuit. However, even in the absence of hardware failures such as a disconnection or a short-circuit, the sensor output value (detection value) or the operation of the battery monitoring unit may sometimes become abnormal due to reduction of an operating supply voltage. When an output value from the sensor or the battery monitoring unit is used as a normal value for control or the like without sensing such abnormalities, the state of the secondary battery cannot be controlled accurately, thereby possibly causing an abnormal operation of the power supply system.